1. Field of the Invention
The present invention relates to a method and apparatus for measuring the angular displacement of a surface and more particularly the invention relates to using Lateral Heterodyne Interferometry (LHI) to measure the angular displacement of a surface.
2. Description of the Prior Art
There has been a long felt need for a non-contact system for measuring the angular displacement of surfaces. This need has been amplified recently with the upcoming manufacture and utilization of the space station. For the space station, long but lightweight structural elements will be utilized to support optical and mechanical components which are required to be precision aligned and kept in precision alignment with respect to each other.
The present applicant is a co-inventor of the subject matter claimed in U.S. Pat. No. 3,930,734 entitled "Process and Apparatus for Sensing Magnitude and Direction of Lateral Displacement" which utilizes Lateral Heterodyne Interferometry to measure linear displacement of slits, gratings and other surfaces which are equipped with periodic perturbations. The technique was extended, in that teaching, to the measurement of the rotation of a disk or drum by measuring the quasi-linear lateral displacement of slits that are placed around the edge of the object that rotates.